Gas turbines have been used in electric power generating plants, in combination with conventional steam power plants. One such arrangement is shown in my U.S. Pat. No. 3,849,662, entitled "Combined Steam and Gas Turbine Power Plant Having Gasified Coal Fuel Supply", which issued on Nov. 19, 1974. In that arrangement, the steam generator is fired continuously with low Btu gas, such as from a coal gasifier, to generate electricity at a constant rate. Excess gas from the coal gasifier is compressed and stored in a storage tank, and during peak periods of electrical demand, it is combusted and used to drive a gas turbine to generate the peak electricity required. With a large storage tank necessary, and also with the gas turbine only being used intermittently, it is a somewhat inefficient power plant with large capital cost. The overall efficiency of a gas turbine is on the order of 75 percent when the residual heat in the exhaust gases is used, while the overall efficiency of a steam generator-turbine is 35-40 percent.